Relief cylinder structure of a multinip calender

ABSTRACT

A relief cylinder structure for guiding a roll in a multinip calender has a frame and an arm that is arranged to move linearly in relation to the frame. A quick-opening cylinder is placed inside the arm. In a fault situation, the relief cylinder causes the cylinder rolls to move rapidly further away from each other. An auxiliary coupling  8  opens in a fault situation, wherein the pressure produced in the quick-opening cylinder  6  is discharged to a hydraulic system in a substantially non-pressurized state. The pressure of the quick-opening cylinder  6  is thus reduced below the pressure of the main cylinder  4,  wherein the auxiliary piston  7  moves towards the end of the arm  3.  Because the volume of the main cylinder  4  grows in accordance with the cylindrical space formed inside the arm  3,  the volume restricted by the frame  2  of the relief cylinder  1  is reduced.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a U.S. national stage application of PCT App. No.PCT/FI03/00452, filed Jun. 9, 2003, the disclosure of which isincorporated by reference herein, and claims priority on FinnishApplication U20020278, Filed Jun. 10, 2002.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

The invention relates to a relief cylinder structure for guiding theroll of a multinip calender. The invention also relates to an arm usedin a relief cylinder structure.

A paper web is calendered by passing it through at least one calendernip. It is a known process to use a so-called soft calender in which theweb is passed through a nip formed by a hard-faced metal roll and asoft-faced roll. The soft-faced roll is typically formed by coating theroll frame with a suitable polymer material.

The calender may also contain several nips successively in the traveldirection of the web. The soft-calender may be composed of twosuccessive pairs of a hard roll and a soft roll. Multinip calenderscomprise several rolls successively, for example on top of each other,and in them the number of rolls is larger than in soft-calenders,typically 6 to 12. In multinip calenders the web travels through nipsformed between successive rolls. Some of the rolls are soft-facedpolymer rolls.

The polymer coating of the calender rolls is an easily damagingcomponent of the machine. If the use of the roll in production continuesin spite of the incipient damage, the damage grows, causes defects inthe production quality (marking of paper), production breaks (unplannedstoppage resulting from the changing of the damaged roll), and in theworst case risks in occupational safety (sudden loosening of the damagedcoating, pieces of coating flying rapidly in the environment).

To be able to prevent damages in the calender in fault situations, therolls of multiroll calenders must be guided rapidly and accurately awayfrom each other in a fault situation. The loading of rolls during use istypically adjusted by means of hydraulic relief cylinders, whereby it isadvantageous to combine quick opening of rolls with the function of therelief cylinders.

Patent publication EP 0 842 324 discloses a relief cylinder structure inwhich the liquid volume of the cylinder can be altered rapidly andaccurately. The basic idea is that the relief cylinder structurecomprises an actual relief cylinder and a quick-opening cylinder thataffect each other by means of an intermediate structure. In a normal usesituation both spaces are in a pressurized state and they both have apredetermined volume. In a fault situation the working pressure isconveyed away from the quick-opening cylinder, wherein the pressure ofthe relief cylinder transfers the intermediate structure and reduces thevolume of the quick-opening cylinder. As a result of thedepressurization of the quick-opening cylinder the total length of theentire cylinder structure is shortened. The shortening takes placerapidly, and its length can be determined accurately by means of thedimensioning of the quick-opening cylinder. In a solution of prior art,the quick-opening cylinder and the control devices necessary for thesame are placed outside the cylinder structure, typically on the side ofthe cylinder structure, said solution requiring a considerable amount ofspace around itself.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a reliefcylinder structure that enables the making of a smaller-sized reliefcylinder structure.

To attain this purpose, the relief cylinder structure according to theinvention is primarily characterized in that said relief cylinderstructure comprises at least a frame, an arm that is arranged to movelinearly in relation to the frame, a quick-opening cylinder and ahydraulic coupling, wherein the quick-opening cylinder is placed insidethe arm.

The invention further relates to an arm used in a relief cylinderstructure, said arm being primarily characterized in that the armcomprises at least a quick-opening cylinder placed therein.

The basic idea of the invention is to implement a relief cylinderstructure in such a manner that its quick-opening cylinder is placedinside the arm of the relief cylinder. By means of the structureaccording to the invention it is in a fault situation possible torapidly change the shape and size of the arm in relation to the maincylinder of the relief cylinder, thus producing a fast movement of thecylinder.

In the normal operating position, a moving piston located in thequick-opening cylinder is in such a position that the volume of thequick-opening cylinder is at its largest, and the end of the armextending towards the main cylinder of the relief cylinder issubstantially straight. The length of the relief cylinder structure isadvantageously adjusted by adjusting the pressure of the main cylinderof the relief cylinder.

In a fault situation, the relief cylinder structure can be shortenedrapidly when the quick-opening cylinder is emptied, i.e. in practice itscontrol valve is opened. Thus, the pressure of the main cylinder pushesthe piston in the quick-opening cylinder towards the end of the arm,wherein the volume of the main cylinder tends to grow. The externalpressing force, however, remains substantially the same and effects thecompression of the structure.

The compression of the structure substantially corresponds to the changein the volume of the quick-opening cylinder, i.e. by means of a smallvolume a small movement is attained and by means of a large volume abroad movement is attained. Because the quick-opening movement isproportional to the volume of the quick-opening cylinder, it is possibleto accurately determine the breadth of the quick-opening movement, andthus to attain a fast and accurate opening movement in case of a faultsituation.

By placing the quick-opening cylinder inside the arm of the reliefcylinder in accordance with the invention, it is possible to attain sucha relief cylinder structure that external devices relating to thequick-opening process are not required in the middle of the same. Bymeans of the relief cylinder structure according to the invention it ispossible to use such solutions in a multinip calender that have not beenpossible in relief cylinder structures of prior art.

Furthermore, the structure of a relief cylinder enabling thequick-opening according to the invention requires a smaller number ofparts, and at the same time it can be implemented more easily thansolutions of prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in more detail withreference to the appended principle drawings.

FIG. 1 shows a relief cylinder according to the invention when thecylinder is in the working position.

FIG. 2 shows the cylinder according to FIG. 1 in the quick-openingposition.

FIG. 3 shows an alternative embodiment of the invention in thequick-opening position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an embodiment of the relief cylinder structure 1 accordingto the invention that comprises a cylinder frame 2 and a piston-like arm3 arranged to move therein. Inside the frame 2, in the area defined bythe arm, an area is formed, for which the term main cylinder 4 will beused hereinbelow. To the main cylinder 4 is connected a hydrauliccoupling 5 placed in the frame 2, the term main coupling 5 being usedhereinbelow for said coupling. The other end of the main coupling 5 isadvantageously placed close to the end of the frame 2, from which it canbe easily connected to the hydraulic system. The gap between the frame 2and the arm 3 is advantageously sealed in a known manner.

According to the invention, a quick-opening cylinder 6 is arrangedinside the arm 3, and an auxiliary piston 7 is arranged to move therein.To the quick-opening cylinder 6 is connected a hydraulic coupling 8, theterm auxiliary coupling 8 being used for said coupling hereinbelow. Theauxiliary coupling 8 is advantageously placed in such a manner that itsother end is positioned close to the end of the arm 3. Thus, theauxiliary coupling 8 can be connected to the hydraulic system in such amanner that the joints are well protected against external damagingfactors.

In the following, the function of a relief cylinder structure 1according to the example will be described in a normal operatingposition according to FIG. 1 and in the quick-opening situation of FIG.2.

In the operating position the relief cylinder structure 1 is typicallyat its longest, wherein the nips between the superimposed rolls of thecalender become as low as possible. In the relief cylinder structure 1according to the invention, pressure is supplied from the hydraulicsystem both to the main coupling 5 and to the auxiliary coupling 8.Thus, the volume of the main cylinder 4 is increased when the arm 3moves in relation to the frame 2 under the influence of the pressureproduced via the main coupling 5, restricted by the counterforceproduced by the roll.

Through the auxiliary coupling 8, pressure is conveyed to thequick-opening cylinder 6, and as a result of this a pressure effect isalso exerted on the auxiliary piston 7. In the normal operating positionat least the same, advantageously a slightly higher pressure is exertedon the quick-opening cylinder 6 than in the main cylinder 4. Thus, theauxiliary piston 7 is positioned in the manner shown in FIG. 1, whereinthe volume of the quick-opening cylinder 6 is at its largest. After thepressure produced in the quick-opening cylinder 6, it is advantageous toclose the hydraulic system leading to the auxiliary coupling 8 in such amanner that said pressure remains in the quick-opening cylinder. Afterthe closing of the above-described pressure system it is advantageous toremove the pressure from said hydraulic system supplying the auxiliarycoupling 8.

The adjustment measures relating to the size of the gap of the nipduring use are advantageously implemented by adjusting the volume of themain cylinder 4 and thus the total length of the relief cylinderstructure 1.

In a fault situation, when it is necessary to transfer the rolls in acontrolled manner and rapidly further away from each other, it istypically not possible to adjust the volume of the main cylinder 4 viathe main coupling 5 because of the substantially too long a period oftime required by the same. In the solution according to the invention,the auxiliary coupling 8 is arranged open in a fault situation, whereinthe pressure produced in the quick-opening cylinder 6 is discharged tothe hydraulic system via the auxiliary coupling 8, said hydraulic systembeing arranged in a substantially non-pressurized state in the mannerdescribed hereinabove. As a result of opening the auxiliary coupling,the pressure of the quick-opening cylinder 6 is reduced below thepressure of the main cylinder 4, wherein the auxiliary piston 7 movestowards the end of the arm 3, to a position according to FIG. 2. Becausethe volume of the main cylinder 4 grows in accordance with thecylindrical space formed inside the arm 3, the volume restricted by theframe 2 of the relief cylinder 1 is reduced with an equal volume. Thus,the arm 3 moves such a distance inside the frame 2 that the volume ofthe main cylinder 4 remains substantially the same as in the operatingsituation, because the force of the roll producing the pressure effectalso remains substantially the same in an operating and fault situation.As a result of the mutual movement of the arm 3 and the frame 2, thelength of the relief cylinder 1 is reduced, wherein the rollcorrespondingly moves into an open position.

Because the opening movement of the relief cylinder attained in thequick opening is proportional to the volume of the quick-openingcylinder 6, it is possible to change the length of the opening movementby changing the volume of the quick-opening cylinder. In a preferredembodiment according to FIG. 3, the length of the auxiliary piston 7 isincreased when compared to the embodiment of FIG. 2. Thus, the volume ofthe quick-opening cylinder 6 is reduced and the quick-opening movement(i.e. the movement of the frame 2 and the arm 3 with respect to eachother) is reduced.

It is advantageous to implement the adjustment of the volume of thequick-opening cylinder 6 in the manner shown in FIGS. 2 and 3 bychanging the length of the auxiliary piston 7, because the frame 2 ofthe relief cylinder 1 and the arm 3 are thus similar, irrespective ofthe volume of the quick-opening cylinder. This is especiallyadvantageous when several different rolls are guided in a multinipcalender according to the invention, because it is possible to determineindividual quick-opening dimensions for the rolls on the basis of thedimensions of the auxiliary pistons 7, and still similar frame parts 2and arm parts 3 of the relief cylinder are used in each roll, whereinmaintenance can be arranged very economically.

It is, of course, obvious that the invention is not limited solely tothe embodiment presented in the example above, but in the quick-openingprocess it is for example possible to guide the pressurized medium fromthe quick-opening cylinder 6 also to another location than to thehydraulic system in a manner deviating from the example. In the reliefcylinder structure 1 according to the invention it is also possible touse any suitable pressurized medium, such as gas or liquid.

1-8. (canceled)
 9. A relief cylinder structure for guiding a roll in amultinip calender, said relief cylinder structure comprising: a frame;an arm arranged to move linearly in relation to the frame, a maincylinder area being defined between the arm and the frame; portions ofthe arm which define a quick-opening cylinder within the arm, thequick-opening cylinder being in communication with the main cylinderarea; and a fluid coupling in communication with the quick-openingcylinder such that fluid within the quick-opening cylinder may bedischarged from the quick-opening cylinder thereby drawing fluid withinthe main cylinder area into the quick-opening cylinder and causing thearm to move within the frame.
 10. The relief cylinder structure of claim9 wherein an auxiliary piston is arranged to move linearly in thequick-opening cylinder, in parallel to the arm and the frame.
 11. Therelief cylinder structure of claim 9 wherein the volume of thequick-opening cylinder is at its largest when the total length of therelief cylinder structure is at its longest.
 12. The relief cylinderstructure of claim 9 wherein the volume of the quick-opening cylinder isat its smallest when the total length of the relief cylinder structureis at its shortest.
 13. The relief cylinder structure of claim 9 whereinthe main fluid coupling is placed substantially at a first end of theframe, and the auxiliary fluid coupling is placed substantially at afirst end of the arm.
 14. A relief cylinder structure for guiding a rollin a multinip calender, the relief cylinder structure comprising: aframe having a main cylinder therewithin; a piston-like arm arranged tomove within the main cylinder of the frame; a main fluid coupling in theframe which communicates with the main cylinder of the frame; portionsof the piston-like arm which define a quick-opening cylinder arrangedinside the arm; an auxiliary piston arranged to move within thequick-opening cylinder; and an auxiliary fluid coupling formed byportions of the arm which communicates with the quick-opening cylinder,wherein in a normal operating position pressure is supplied through theauxiliary fluid coupling to the quick-opening cylinder and through themain fluid coupling to the main cylinder, both said supplied pressuresacting upon the auxiliary piston, and wherein in a fault situation, theauxiliary fluid coupling is arranged to be open, wherein the pressureproduced in the quick-opening cylinder is discharged to a fluid systemvia the auxiliary fluid coupling, said fluid system being arranged in asubstantially non-pressurized state, as a result of opening theauxiliary coupling, the pressure of the quick-opening cylinder isreduced below the pressure of the main cylinder, wherein the auxiliarypiston moves within the quick-opening cylinder to increase the volume ofthe quick-opening cylinder in communication with the main cylinder, suchthat the piston-like arm is retracted within the frame reducing thelength of the relief cylinder.
 15. The structure of claim 14 wherein theauxiliary piston is arranged to move linearly in the quick-openingcylinder, in parallel to the arm and the frame.
 16. A relief cylinderstructure for guiding a roll in a multinip calender, said reliefcylinder structure comprising: a frame having portions defining aninterior volume; an arm arranged to move linearly in relation to theframe, and having portions which extend into the frame interior volumeto define a main cylinder area between the arm and the frame; a mainfluid coupling which is in communication with the main cylinder area,wherein introduction of fluid through the main fluid coupling into themain cylinder area causes the arm to move in the frame; portions of thearm which define a quick-opening cylinder interior volume; an auxiliaryfluid coupling which is in communication with the quick-opening cylinderinterior volume; and an auxiliary piston which is movable within thequick-opening cylinder interior volume, the auxiliary piston dividingthe quick-opening cylinder interior volume into two portions which aresealed from one another by the auxiliary piston, a first volume which isin communication with the auxiliary fluid coupling, and a second volumewhich is in communication with the main cylinder area, the sizes of thefirst volume and the second volume being variable with the movement ofthe auxiliary piston.
 17. The relief cylinder structure of claim 16wherein the auxiliary piston is arranged to move linearly in thequick-opening cylinder interior volume, in parallel to the arm and theframe.
 18. The relief cylinder structure of claim 16 wherein the mainfluid coupling is placed substantially at a first end of the frame, andthe auxiliary fluid coupling is placed substantially at a first end ofthe arm.
 19. The relief cylinder structure for guiding a roll in amultinip calender of claim 16 further comprising a second reliefcylinder structure within the same multinip calender, wherein the secondrelief cylinder structure has a second auxiliary piston of a lengthdifferent than the other relief cylinder structure auxiliary piston.